The invention relates to a reversing alarm apparatus for a work vehicle, and more particularly, to a reversing alarm apparatus for a work vehicle, which detects reversing operation of a vehicle forward and reverse travel operating lever to transmit a vehicle reversing alarm in a vehicle forward and reverse travel operating lever device for performing speed control proportional to a magnitude of an operating stroke of the forward and reverse travel operating lever.
Conventionally, many work vehicles mount thereon a reversing alarm device for a work vehicle. Therefore, in a work vehicle, in which a traveling speed is controlled in proportion to a magnitude of an operating stroke of a forward and reverse travel operating lever, a vehicle reversing alarm is issued upon detection of reversing operation of the forward and reverse travel operating lever.
The prior art disclosed in, for example, Japanese Patent Laid-Open No. 80449/1996, s well known and a circuit diagram described in the publication is shown in FIGS. 5 to 7. With a first prior art of the publication, provided near a forward and reverse travel operating lever 32 for operating a direction switching valve 31, which controls a traveling motor 30, as shown in FIG. 5 is a limit switch 33 for detecting the reversing operation of the forward and reverse travel operating lever 32, so that a signal from the limit switch 33 is used to detect the reversing operation of a vehicle to issue a reversing alarm. Also, with a second prior art of the publication, a pressure switch 35 is provided in an operating pressure circuit 34 at the time of reverse traveling rotation of the traveling motor 30 as shown in FIG. 6, so that a signal from the pressure switch 35 is used to detect the reversing operation of a vehicle to issue a reversing alarm. Further, with a third prior art of the publication, a pressure switch 39 is provided in a reverse travel operating pilot pressure circuit 38 of a pilot valve 37 for operating a pilot direction switching valve 36, which serves for the forward and reverse travel operation and controls the traveling motor 30, as shown in FIG. 7, so that a signal from the pressure switch 39 is used to detect the reversing operation of a vehicle to issue a reversing alarm.
However, the prior art disclosed in the above-mentioned Japanese Patent Laid-Open No. 80449/1996 involves the following problems.
In the first prior art, in which the limit switch 33 detects the reversing operation of the forward and reverse travel operating lever 32, there is a need of applying an operating force required for pushing a detection rod (a roller adapted to be pushed when contacted by a cam or the like) of the limit switch 33 at the time of reversing operation of the forward and reverse travel operating lever 32. However, the limit switch 33 used in construction machines or the like is ordinarily strongly-built to have durability according to severe circumstances and use in work site, so that a large operating force must be applied to push the detecting rod of the limit switch 33 at the start of reversing operation, which would cause the possibility that after such pushing the detecting rod makes a stroke beyond a desired stroke position to attain an unexpected reversing speed. Also, since the limit switch 33 is not contacted in forward travel operation but rather contacted in reverse travel operation, there is caused a problem that the forward and reverse operating forces become uneven to make an operating feeling of the forward and reverse travel operating lever 32 unfavorable and, in particular, to make a minute reversing operation difficult.
In the second and third prior arts, in which the pressure switch detects the reverse travel acting pressure and the reverse travel operating pilot pressure of the traveling motor 30, there are caused problems that a stable detecting action cannot be obtained under the influence of oil temperature and pulsation of a pressure fluid and that even after the reversing operation of the travel operating lever is stopped, a residual pressure of the pressure fluid maintains a state of detecting operation by the pressure switch to cause sounding of a reverse alarm.
In order to improve the above-mentioned problems involved in the prior technical means, in which the reversing operation of the forward and reverse travel operating lever is indirectly grasped by a limit switch or detection of the reversing operating pilot pressure or the reversing drive pressure of a traveling drive system to sound a reversing alarm, the invention has its object to provide a reversing alarm apparatus of a work vehicle, in which reversing can be operated without application of a surplus reversing operating force at the time of reversing operation of a forward and reverse travel operating lever, and movements of the forward and reverse travel operating lever are directly detected to sound a reversing alarm.
In order to attain the above-mentioned object, the first invention provides a reversing alarm apparatus for a work vehicle provided with a forward and reverse travel operating lever device to output a forward and reverse speed command signal in accordance with an amount of an operating stroke, wherein a reversing alarm of the work vehicle is issued by a reversing operation detecting device composed of a non-contact type sensor and provided on the forward and reverse travel operating lever device.
According to the first feature of the invention, since the non-contact type sensor detects movements in the reversing operation of the forward and reverse travel operating lever and there is caused no contact between the forward and reverse travel operating lever and the sensor, no change in lever operating forces is caused at the time of reversing operation and operating forces in forward and reverse travel can be made substantially uniform not to injure the operating feeling. Also, the reversing operation is possible with small operating forces to enable improving a minute operability.
Further, since the non-contact type sensor directly detects movements in reversing operation of the forward and reverse travel-operating lever, it is possible to make sure that a reversing alarm is issued and stopped in cooperation with a lever operating action.
The second feature of the invention provides a reversing alarm apparatus for a works vehicle, in which the reversing operation detecting device of the first invention is constructed such that the non-contact type sensor is installed with a sensor detecting surface facing in a direction parallel to a forward and reverse rotation shaft of a forward and reverse travel operating lever, and the reversing operation detecting device is composed of a detected lever linkage mechanism which swings vertically in a plane perpendicular to the forward and reverse rotation shaft following rotation of the forward and reverse rotation shaft of the forward and reverse travel operating lever to intersect a sensor signal of the non-contact type sensor.
According to the second invention, since the detected lever linkage mechanism is designed to follow the reverse travel operation of the forward and reverse travel operating lever to intersect the non-contact type sensor and to follow the forward travel operation not to intersect the non-contact type sensor, the forward travel operation is not detected.
The third aspect of the invention provides a reversing alarm apparatus for a work vehicle, in which the detected lever linkage mechanism of the reversing operation detecting device of the second invention is constructed such that the detected lever linkage mechanism of the reversing operation detecting device comprises a rotation interlocking lever mounted on the forward and reverse rotation shaft of the forward and reverse travel operating lever, and a seesaw movement lever, which includes on one side thereof a lever portion having an elongated hole and on the other side thereof a detected lever portion intersecting the non-contact type sensor, and the rotation interlocking lever serves as a linkage mechanism for connection of the rotation interlocking lever such that a point of engaging cooperation slides in the elongated hole of the seesaw movement lever.
According to the third invention, since the forward and reverse operating rotation interlocking lever mounted on the forward and reverse rotation shaft of the forward and reverse travel operating lever, and the seesaw movement lever are connected to and combined with the non-contact type sensor and the point of engaging cooperation is slidingly moved, there is an advantage that the lever swinging ratio of the seesaw movement lever can be made small as compared with a swinging stroke of the forward and reverse operating rotation interlocking lever and the reversing operation detecting device can be installed in a compact space near the forward and reverse travel operating lever.
The fourth feature of the invention provides a reversing alarm apparatus for a work vehicle, in which the point of engaging cooperation between the seesaw movement lever and the forward and reverse operating rotation interlocking lever in the third invention cooperates in a position close to a seesaw fulcrum when the forward and reverse operating rotation interlocking lever is located in a forward and reverse travel operating neutral turning position, and slides in a direction away from the seesaw fulcrum when the forward and reverse operating rotation interlocking lever turns in a direction of forward and reverse travel operation from the forward and reverse travel operating neutral turning position.
According to the fourth feature of the invention, when the forward and reverse travel-operating lever is operated reversely, the seesaw movement lever is swung from a position where the point of engaging cooperation between the seesaw movement lever and the forward and reverse operating rotation interlocking lever is near the seesaw movement lever fulcrum, a location where the seesaw movement lever is not detected is rapidly entered in the detection range of the non-contact type sensor to enable issuing a reversing alarm without being late for the reversing operation of the forward and reverse travel-operating lever.